1. Field of the Invention
The invention relates to the field of propulsion systems for lighter-than-air vehicles and, in particular, to a propulsion system that provides maneuvering and thrust vectoring control.
2. Description of Related Art
There are three general types of non-rigid vehicles: those comprising a single gas filled bag; several gasbags joined together in series; and, of course, those having a multiple number gasbags within a non-rigid envelope. A particular problem with such non-rigid vehicles is that, because of the lack of rigid structure within the gasbag, the placement of the thrust assemblies is limited to the gondola. Thus, because the gondola is suspended from the bottom of the vehicle, any maneuvering forces generated by the propulsion system can not act through the center of pressure of the vehicle and, therefore, their effectiveness is reduced. This is also generally true of rigid airships that have an internal structure defining the shape of the vehicle that contain a plurality of gasbags with an aerodynamic cover there over. Even though the propulsion system can be mounted almost anywhere on the rigid structure, they are most often mounted at or near the bottom of the vehicle for ease of access, etc. Thus what is needed is a propulsion system wherein all these control problems are addressed while inducing a minimum weight addition to the vehicle. Another major problem with both rigid and non-rigid lighter-than-air vehicles is their limited ability to station keep and/or maneuver when docking, especially if there are any significant cross-winds. This is due primarily to their large cross-sectional area, which causes the vehicle to "weather vane" and "wave" with the wind. They are particularly difficult to control if the wind is gusting or when there are significant up or down drafts. In fact, docking has proven to be the most difficult portion of a flight for a lighter-than-air-vehicle.
In the past reversible propellers have been used to provide braking as well as differential thrust for directional control, but have proven to be only marginally effective. Side thrusters in the form of ducted fans or propellers are more effective, but when dedicated solely for docking and "take off", the vehicle clearly incurs a significant weight penalty. Examples of these can be found in U.S. Pat. Nos. 1,876,153, "Aerial Transportation Apparatus" by S. O. Spurrier and 4,402,475, "Thrusters for Airship Control" by V. H. Pavlecka. Dedicated vertical lift propellers have also been used to provide additional lift at take off; however, the same weight penalty is encountered. Examples of these can be found in U.S. Pat. Nos. 1,677,688, "Aircraft" by A. Rees and 5,026,003, "Lighter-Than-Air Aircraft" by W. R. Smith.
Another approach has been the use of ducted and unducted propellers that can rotate from a position aligned with the longitudinal axis of the vehicle to a vertical position. This system, while providing upward and downward thrust, do not provide side thrust. Another disadvantage is the fact that, if the ducted fans are mounted on the cargo compartment or gondola, the exhaust therefrom will strike the gasbag when providing downward thrust, unless they are mounted on extremely long pylons. Furthermore, if the vehicle is very large, the ducted fans and the powerplants therefore, must also be large to provide sufficient cruising speed. This can create structural weight problems if the powerplants are integral with the ducted fans, for the mechanism for supporting and rotating the combination ducted fan and powerplant becomes quite large. Examples of rotatatable thruster can be found in British Patent Nos. 26,897, "Improvements In The Propulsion Of Aerial Or Water Vehicles by J. Macinante and 2,250,007A, "Aerobatic Airship" by S. Omiya, and U.S. Pat. Nos. 1,019,635, Adjustable Propeller" by F. Harlow, 1,868,976, "Aircraft Propelling Mechanism" by C. S. Hall, 1,879,345, Dirigible Air Sailing Craft" by A. H. Lawrence and 4,891,029, "Remote Control Lighter-Than-Air Toy" by J. M. Hutchinson.
In co-pending U.S. Pat. application Ser. No. 08/108280 "Propulsion System For A Lighter-Than-Air Vehicle" by J. B. Kalisz, et. al. a more versatile system is provided. This invention includes a pylon having a longitudinal axis and first and second ends, the first end of the pylon is rotatably mounted to the vehicle with the second end extending outward therefrom. The pylon is rotatable about its first end in a plane perpendicular to the longitudinal axis of the vehicle. A thrust producing assembly is mounted on the second end of the pylon and is rotatable about an axis of rotation in a plane perpendicular to the longitudinal axis of the pylon. A powerplant assembly is coupled to the thrust producing assembly to provide power thereto. Thus with the Kalisz,et al. invention, the pylon can be rotated 45 degrees downward and the thrust assembly can be rotated 90 degrees downward. This allows the exhaust from the thrust assembly to miss the gasbag. Additionally, the pylon can be rotated upward so that the thrust assembly is "out of the way" when the vehicle is docked. In both these inventions, the powerplant is preferably mounted on the vehicle (gondola) and is coupled by shafting to the thrust assembly, in the Kalisz, et. al. invention the shafting extends through the pylon. Alternately the powerplant could be mounted directly with the thrust assembly. U.S. Pat. Nos. 3,614,034, "V/STOL Aircraft" by R. E. Townsend and 3,451,648, "Aircraft Having Movable Engines For Vertical Take-Off And Landing" by O. E. Pabst, et al. disclose systems for retractable lift fans for Aircraft wherein dedicated lift engines are rotatable on support structure from a internally stored position to operation positions.
The problem is providing fuel efficient cruise powerplants and yet provide the high power required for docking, a two to one difference in power requirements. The proposed solution in the above two patent applications is to use a greater number of propulsion systems having fuel efficient diesel engines mounted in the gondola. However, mounting large diesel engines on the end of the pylon creates a significant weight penalty. Using turboshaft engines, that have very high thrust to weight ratios, mounted directly to the thrust assembly provides the required thrust for docking maneuvers, but cruise efficiency is be reduced.
Thus it is a primary object of the subject invention to provide a propulsion system for a lighter-than-air vehicle.
It is another primary object of the subject invention to provide a propulsion system for a lighter-than-air vehicle that provides increased maneuvering capability.
It is another primary object of the subject invention to provide a propulsion system that is both fuel efficient at cruise and also can provide the necessary increased thrust necessary during docking.
It is a further object of the subject invention to provide a propulsion system for a lighter-than-air vehicle that provides for the repositioning of the thrust producing assemblies, such as ducted and unducted fans or propellers, so that side thrust can be provided without exhaust therefrom striking the gasbag of the vehicle.
It is another object of the subject invention to provide a propulsion system for a lighter-than-air vehicle wherein the thrust producing assemblies, such as ducted and unducted and fans or propellers, can be positioned so as not to interfere with ground handling equipment when docking.